Absolutely no acceptable connection with WUSB54GC

We have a new house for about two weeks now and i thought...
Lets setup a wireless trough the whole house. We have a HP dv9000 laptop with Vista and a desktop with XP Pro SP2. I was thinking that it would be wonderfull to have wireless connection so i don't have to place many meters of cable through the house...

Last week i bought this router: Wireless-N router WRT160N
With my laptop i had absolutely no problems connecting the router and after a restart i was on the internet with maximum speed.

Now i went upstairs (first floor) and connected the desktop by wire to the router to setup and make connection. This turned out positive and after a restart i installed the software of my new wireless WUSB54GC adapter:
I restart my system, connect my USB adapter and the computer is searching for connection.
In a list he found several wireless connections from people in my neighbourhood, but no connection of me.
I tried to add the connection manual and i still cant surf on the internet via the router.
I de-installed everything, installed again, restarted etc etc
With the result i still have no connection on my desktop computer.
In the beginning the USB adapter saw my router, but the last couple of days he doenst see him anymore...

Should i take this wireless adapter back to the store or is there an easy way to have access with my router by this usb adapter and surf on the internet.
As the desktop is my workstation and my profession is webdesign, i really would like to have internet on it.

Hope there is a good sollution for it. I have three days left to get my money back from the store where i bought the USB adapter.